James Cameron Dives to Deepest Depths of the Ocean, Bobs Back Up After Hydraulic Leak UPDATED

Explorer/filmmaker James Cameron tweeted his readiness to voyage to the bottom of the sea in the Mariana Trench on Saturday– 6.8 miles, down to the deepest ocean territory he depicted in his fictional film "The Abyss"–but Sunday he did it for real. And he plumbed the depths of "The Challenger Deep" squeezed alone into a specially crafted submersible ("Deepsea Challenger") that he helped to design as a vertical, rather than horizontal diving torpedo. Cameron’s first words on reaching the bottom: “All systems OK.”

He also tweeted @DeepChallenge: "Just arrived at the ocean's deepest pt. Hitting bottom never felt so good. Can't wait to share what I'm seeing w/ you."

UPDATE: At noon Western Pacific time (10 p.m. ET), Cameron's sub reemerged from the deep and he climbed out. Billionaire Paul Allen's hovering helicopter spotted the sub when it broke the surface. The sub took two hours 36 minutes to descend but only 70 minutes to come back up. Timing and weather conditions were both ideal–but a squall was on the horizon. Detailed National Geographic story here.

The National Geographic Explorer-in-Residence reached the “Challenger Deep,” the lowest part of the ocean, on Monday, March 26, at 7:52 a.m. local time (Sunday, March 25, 5:52 p.m. Eastern Time). The depth was recorded at 35,756 feet. The plan was for the 57-year-old six-foot two explorer to spend up to six hours on the floor of the Pacific Ocean, collecting samples with a robotic claw for scientific research and taking photos and video of the Mariana Trench. UPDATE: It was dull down there–no fish. "I didn't feel like I got to a place where I could take interesting geology samples or found anything interesting biologically," Cameron reported later. He had to come up three hours early because of a hydraulic leak.

Cameron has long innovated with submersibles and robotic underwater cameras for a series of deep sea documentaries, including dives to the Titanic. (I interviewed Cameron on his new frontiers at Popular Mechanics here. For National Geographic coverage on the dive, go here. Follow it on Twitter: @DeepChallenge, #deepseachallenge, and on Facebook.)

DEEPSEA CHALLENGE — a joint scientific expedition by Cameron, National Geographic and Rolex–backed the dive. Their goal is to "conduct deep-ocean research and exploration." Cameron is the only person to ever complete the dive to the “Challenger Deep” solo, and the first since 1960 to reach the deepest point in the world in a manned submersible, when the feat was completed by U.S. Navy Lt. Don Walsh and Swiss oceanographer Jacques Piccard in the bathyscaphe Trieste.